And the FBI/­Hungarian National Police Organized Crime Task Force has been up and running for five years, working to dismantle organized crime groups. Just last month, we obtained approval to have FBI agents permanently stationed here in Budapest to work on the Task Force.

The Task Force has had a number of successes. Right here in Budapest , Ukranian-­born Semion Mogilevich established the headquarters of his powerful organized crime enterprise. The group engaged in drug and weapons trafficking, prostitution, and money laundering, and organized stock fraud in the United States and Canada in which investors lost over $150 million.

As soon as the Task Force began investigating his activities, Mogilevich realized he could no longer use Budapest as his base of operations. He immediately fled the country, and is now hiding in Moscow. Working closely with Hungarian authorities, United States prosecutors obtained a 45-­count indictment against Mogilevich and three other criminals, charging them with money laundering, securities fraud, and racketeering.

Mueller’s biographer, Garrett Graff, called the Budapest task force “perhaps the most unique FBI force in the world.” Hungary was the only country outside Afghanistan and Iraq where agents were permanently stationed.

The Budapest task force assembled a global picture of Mogilevich’s operation. According to a Dec. 22, 2006 report in The Wall Street Journal, FBI agents in Budapest got help from authorities in Israel, another of Mr. Mogilevich’s suspected bases of operations, and Cyprus, an offshore banking center used by many Russians.

The full extent of Mogilevich’s US ties are still unknown. Although banned from entering the country because of his alleged criminal ties, Mogilevich has visited Boston, Philadelphia, and Miami under aliases to meet with U.S. associates, and the FBI photographed at least one of his aides attending a Republican Party fundraiser in Texas.

Mogilevich was arrested in Moscow in 2008 and then subsequently released him the following year. He lives more or less openly in Russia today. While US eventually caught up with Osama bin Laden, Mogilevich was the one who got away.

Mueller’s role as special counsel for Trump’s Russia links may be a second chance of sorts. By probing Trump’s links to Mogilevich, Mueller may be able to snare an even bigger fish.